1. Field of the Invention
This invention relates to an electric control apparatus and more specifically to an electric control apparatus using a magnetic-field source and a magnetic-to-electric transducer which can be applied to various devices such as a throttle position sensor.
2. Description of the Prior Art
In some automotive vehicles, the position of a throttle valve is detected by a throttle position sensor, and a vehicle-driving engine is controlled in response to the detected position of the throttle valve.
Japanese published unexamined patent application 2-298815 discloses a rotational angle sensor used as a throttle position sensor of a noncontact type. In the throttle position sensor of Japanese patent application 2-298815, a magnetoresistive element is formed on a base of a magnetic sensor, and a magnet is provided at the fore end of a shaft gearing with a throttle valve. The magnet is disposed at a position opposing or facing the magnetoresistive element. A magnetic field of a uniform flux density is developed between an N pole and an S pole on arms of arms the magnet. The magnetoresistive element is exposed to a portion of the magnetic field. As the shaft gearing with the throttle valve rotates with the rotation of the throttle valve, the magnetic field rotates and hence the resistance of the magnetoresistive element varies. The resistance of the magnetoresistive element so detected indicated of the angular position of the throttle valve.
In cases where the output signal of such a throttle position sensor is used for engine control, it is desirable to detect a malfunction of the sensor and to provide a countermeasure against the detected malfunction to attain a fail-safe function. Japanese patent application 2-298815 does not teach the detection of a malfunction of the throttle position sensor.
Japanese published unexamined patent application 64-37607 discloses a throttle position sensor having a storage space within a throttle body. A connector is fitted to the storage space. A magnetic sensitive element fixed on the connector opposes a permanent magnet. The magnetic sensitive element has a pattern face which is approximately parallel to a magnetic field generated by the permanent magnet. The permanent magnet rotates together with the throttle valve. The magnetic field detected by the magnetic sensitive element varies in accordance with rotation of the throttle valve. Thus, the detection of the magnetic field provides an indication of the angular position of the throttle valve. Japanese patent application 2-298815 does not teach the detection of a malfunction of the throttle position sensor.